Electronic components such as semiconductor chips are becoming progressively smaller with successive new product releases, while at the same time heat dissipation requirements thereof are increasing. Commonly, a thermal interface material is utilized between the electronic component and a heat sink in order to efficiently dissipate heat generated by the electronic component.
A conventional thermal interface material is made by diffusing particles with a high heat conduction coefficient in a base material. The particles can be made of graphite, boron nitride, silicon oxide, alumina, silver, or other metals. However, a heat conduction coefficient of this kind of thermal interface material is now considered to be too low for many contemporary applications, because it cannot adequately meet the heat dissipation requirements of modern electronic components.
An article entitled “Unusually High Thermal Conductivity of Carbon Nanotubes” and authored by Savas Berber (page 4613, Vol. 84, Physical Review Letters 2000) discloses that a heat conduction coefficient of a carbon nanotube can be 6600 W/m·K (watts/meter·Kelvin) at room temperature.
A kind of thermal interface material which conducts heat by using carbon nanotubes has been developed. The thermal interface material is formed by injection molding, and has a plurality of carbon nanotubes incorporated in a matrix material. A first surface of the thermal interface material engages with an electronic device, and an opposite second surface of the thermal interface material engages with a heat sink. The second surface has a larger area than the first surface, so that heat can be uniformly spread over the larger second surface. However, the thermal interface material is generally formed by injection molding, and is relatively thick. This increases a bulk of the thermal interface material and reduces its flexibility. Furthermore, the carbon nanotubes are disposed in the matrix material randomly and multidirectionally. This means that heat does not necessarily spread uniformly through the thermal interface material. In addition, the heat does not necessarily spread directly from the first surface engaged with the electronic device to the second surface engaged with the heat sink.
To overcome the above-described problems, a method for producing a thermal interface structure having aligned carbon nanotubes has been developed. In a batch process, a capacitor is immersed in a bath of a slurry of thermoplastic polymer containing randomly oriented carbon nanotubes, and capacitor plates are adjusted to a desired spacing between them to provide a particular film thickness. Prior to curing of a preform of the thermal interface structure, the preform is energized to create an electrical field to orient the carbon nanotubes in a uniform direction in the polymer. Upon curing, the carbon nanotubes are embedded in the polymer in the desired alignment.
However, even though the thermal interface structure's thermal conductivity may be enhanced, it still may not be satisfactory for some applications. It is believed that one important reason limiting the thermal conductivity is the existence of thermal interface resistance where adjacent carbon nanotubes in any given heat conduction path within the thermal interface structure adjoin each other. In particular, where a heat conduction path comprises a plurality of such thermal interface resistance junctions, the overall thermal resistance along the entire heat conduction path may be significant.
What is needed, therefore, is a thermal interface material with good thermal conductivity. What is also needed is a method for manufacturing such kind of thermal interface material.